The ropes have blessed silver thread woven into them, so Stephen can’t break them. Jon just gets his hands tied, because Jon is not fast enough to dodge a bullet.
Stephen: This is not how I imagined it would feel to have a woman tie me up.
Jon: You’ve never imagined a woman tying you up, Stephen.
Stephen: I might have! You don’t know!
Heinkel: Sister? Knock him out.